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    <span class="token keyword">function</span> <span class="token function">boundFn</span><span class="token punctuation">(</span><span class="token parameter">a</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>        
        <span class="token keyword">var</span> l <span class="token operator">=</span> arguments<span class="token punctuation">.</span>length<span class="token punctuation">;</span>        
        <span class="token keyword">return</span> l <span class="token operator">?</span>
            <span class="token punctuation">(</span>
                l <span class="token operator">&gt;</span> <span class="token number">1</span> <span class="token operator">?</span>
                <span class="token function">fn</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span>ctx<span class="token punctuation">,</span> arguments<span class="token punctuation">)</span> <span class="token operator">:</span>
                <span class="token function">fn</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>ctx<span class="token punctuation">,</span> a<span class="token punctuation">)</span>
            <span class="token punctuation">)</span><span class="token operator">:</span>
            <span class="token function">fn</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>ctx<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
    boundFn<span class="token punctuation">.</span>_length <span class="token operator">=</span> fn<span class="token punctuation">.</span>length<span class="token punctuation">;</span>    
    <span class="token keyword">return</span> boundFn
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token function">nativeBind</span><span class="token punctuation">(</span><span class="token parameter">fn<span class="token punctuation">,</span> ctx</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>    
    <span class="token keyword">return</span> <span class="token function">fn</span><span class="token punctuation">.</span><span class="token function">bind</span><span class="token punctuation">(</span>ctx<span class="token punctuation">)</span>

<span class="token punctuation">}</span>

<span class="token keyword">var</span> bind <span class="token operator">=</span> <span class="token class-name">Function</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span>bind <span class="token operator">?</span>
    nativeBind <span class="token operator">:</span>
    polyfillBind<span class="token punctuation">;</span>
</code></pre></div><ul><li><code>methods</code>确定上下文执行环境是通过<code>bind</code>绑定的。</li> <li>考虑到不是所有浏览器都支持<code>bind</code>,所以做了兼容，采用<code>apply 和 call</code>.</li></ul> <h2 id="methods-通过以下方法实现对实例的访问"><a href="#methods-通过以下方法实现对实例的访问" class="header-anchor">#</a> methods 通过以下方法实现对实例的访问</h2> <div class="language-javascript extra-class"><pre class="language-javascript"><code><span class="token keyword">function</span> <span class="token function">initMethods</span><span class="token punctuation">(</span><span class="token parameter">vm<span class="token punctuation">,</span> methods</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>    
    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">var</span> key <span class="token keyword">in</span> methods<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        vm<span class="token punctuation">[</span>key<span class="token punctuation">]</span> <span class="token operator">=</span> 
            methods<span class="token punctuation">[</span>key<span class="token punctuation">]</span> <span class="token operator">==</span> <span class="token keyword">null</span> <span class="token operator">?</span> 
            noop <span class="token operator">:</span> 
            <span class="token function">bind</span><span class="token punctuation">(</span>methods<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">,</span> vm<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">最后一次修改时间:</span> <span class="time">9/28/2020, 11:37:23 AM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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